Field
Embodiments of the disclosure generally relate to a corner spoiler for improving profile uniformity and method for distributing gas in a processing chamber.
Description of the Background Art
Liquid crystal displays or flat panels are commonly used for active matrix displays such as computer and television monitors. Plasma enhanced chemical vapor deposition (PECVD) is generally employed to deposit thin films on a substrate such as a transparent substrate for flat panel display or semiconductor wafer. PECVD is generally accomplished by introducing a precursor gas or gas mixture, e.g., silane (SiH4) and nitrogen (N2), into a vacuum chamber that contains a substrate. The precursor gas or gas mixture is typically directed downwardly through a distribution plate situated near the top of the chamber. The precursor gas or gas mixture in the chamber is energized (e.g., excited) into a plasma by applying radio frequency (RF) power to the chamber from one or more RF sources coupled to the chamber. The excited gas or gas mixture reacts to form a layer of material, e.g., silicon nitride (SiNx), on a surface of the substrate that is positioned on a temperature controlled substrate support. The silicon nitride layer forms passivation layers, gate insulators, and/or buffer layers for a low temperature poly silicon (LTPS) film stack in the next generation thin film transistors (TFT) and active matrix organic light emitting diodes (AMOLED). TFT and AMOLED are but two types of devices for forming flat panel displays.
Flat panels processed by PECVD techniques are typically large, often exceeding 4 square meters. As the size of substrates continues to grow in the flat panel display industry, film thickness and film uniformity control for large area PECVD becomes an issue. Further, as the substrates are rectangular, edges of the substrate, such as sides and corners thereof, experience conditions that may be different than the conditions experienced at other portions of the substrate. For example, centrally located plasma increases the deposition rate at the corners of the substrate, resulting in “corner peaks”. The corner peaks adversely affect processing parameters, such as film thickness, and increase the edge exclusion range. Overall film thickness affects the drain current and the threshold voltage of the flat panel.
Conventional techniques for controlling the deposition rate include modulating the flow of the gas through the gas distribution plate and changing the material of chamber components to affect the impedance of the plasma distribution. However, conventional techniques are often costly and only capable of changing the film uniformity profile at a larger range, e.g., greater than 300 mm from the corner of the substrate.
Therefore, there is a need for improving the deposition rate and film thickness uniformity in substrates, particularly at the corner regions of the substrate.